失重条件下人体姿态控制动作分析

本文建立了失重人体主体和上、下肢的一般性动力学方程，将主体姿态的六维复杂运动简化为三个三维简单运动。通过分析、计算和动力学仿真直观地描述了用简单动作控制失重人体姿态的可行性和可操作性。     

美国失重生理在轨研究证据分析与评价

自1961年4月12日苏联航天员加加林乘“东方1号”飞船首次进入太空以来,科学家们就开始采用各种手段和方法监测人体在失重环境中的生理变化,随着对失重生理效应认识的逐步深入以及载人飞行时间的延长,各种防护理念、防护措施以及防护效果的评估也逐步推进.本文系统地回顾了载人航天以来美国各次飞行任务的在轨失重生理学研究以及防护措施的评价,旨在为我国载人空间站的建设提供借鉴.     

失重对航天员健康的影响

大家都知道,生活在地球上的人们,除了在某些特殊场合(如乘坐飞机时等)会经历一些短暂的重力变化外,从出生到死亡都始终处于相同的重力环境中。人类的全部生理特点的形成都与地球表面的重力密切相关。但是,在太空中,作用于人体的重力将会消失(即失重),航天员们要在没有重力(即失重)的环境下度过数日、甚至是数月的太空生活。失重会引起航天员一系列的生理改变,虽然这些变化大多是人体为了适应失重环境而产生的调节性改变,然而,也有一些已达到临床病理变化的水平。这些变化不仅会给航天员的健康带来危害,甚至还会间接影响航天飞行任务的顺利完…     

失重/模拟失重对真菌影响的研究进展

随着载人航天器的发射,人体及航天器将不可避免地携带真菌到太空环境中。目前已发现空间站、航天器以及航天员身上存在多种真菌。在失重环境下,人体免疫力会降低,一些致病真菌的生物学性状会发生变化,潜在致病性增强,对航天员的健康构成威胁。本文主要就近年来模拟失重及太空环境条件下几种常见真菌的形态结构、增殖、毒力、耐药性的影响进行综述。研究表明,太空环境和模拟失重环境可使真菌形态结构发生变化,促进大部分真菌增殖,可使部分真菌毒性和耐药性增强,但相关生物学性状及形成机制还有很多不确定性,如毒力和耐药性,有待深入研究。     

航天员的心理障碍

航天员的心理障碍唐友昌，沈羡云遨游太空，俯瞰尘寰，着实令人神往。但在茫茫太空，生活在小小航天器仓室中的航天员们，却会产生抑制不了的孤独感、烦闷感和恐惧感。在太空这个地狱般黑暗和极冷世界生活的人，处于“绝对的孤独和与世隔绝”状态，失重和黑色会使他们产生...     

载人航天60问(5)

20.人在太空中味觉有何改变?在太空的失重环境中,人的味觉也会发生改变:吃任何东西都感到淡而无味。首先发现此现象的是美国“天空实验室-3”号上的航天员洛斯马等人。在飞行中,他们带上了很多辛辣的食物以增进食欲,但吃时忽然发现他们的味觉变了,无法品评出这些食物的味道。1978年,前苏联航天员在为期5个月的空间飞行中对平时极爱吃的面包、火腿都没有了食欲,很想吃果酱、蜂蜜等甜食,后来供给飞船为他们专门送去了大蒜、洋葱、蜂蜜和芥末都具刺激性的食品。前苏联在“联盟”30号和“联盟”31号飞船上安装了一种名叫电子味觉测量仪的装置,研…     

载人航天60问(6)

27.航天飞行对生殖生育有影响吗?早在上个世纪60年代,前苏联的生物卫星就曾送老鼠上天“结婚”,让雌鼠在太空中怀孕和分娩获得成功。美国也加强了这方面的研究,尤其是长期太空飞行任务提出后,有关这方面的实验就更多了。他们先后将鼠送上天,研究胚胎在太空中孕育和生长的全过程,结论是:动物可以在太空中怀孕和生育,但幼鼠的骨骼脆弱,容易折断,肌肉也松弛无力。当将鼠放在一个产生重力的小离心机上,用离心机旋转产生的离心力来替代地心引力时,这种情况就消除了,这说明重力消失对运动的生长还是有一定影响的。长期在太空生活对人的生殖是否有…     

失重对人的压力感受反射功能的影响

失重可引起航天员心血管功能失调,表现为返回后立位时血压的降低、心率的异常及运动耐力下降。由于压力突然改变时压力感受器反射功能在调节血液动力学上起主要作用,因此在研究失重心血管系统失调的起因时,必须了解失重对压力感受器反射功能的影响。本实验观察了7名SLS-1航天飞机飞行员在飞行前、中、后时压力感受器反射功能的变化。具体的测量时     

航天适应性综合征

航天适应性综合征沈羡云人从长期生存和适应的ＩＧ环境中，突然进入到太空的失重环境，体内的生理系统出现一系列适应性反应，这些适应性反应所表现的症状称为“航天适应性综合征”（ＳＡＳ）．航天适应性综合症的表现头面部充血及头痛航天员进入到失重环境中，由于血液头...     

失重/模拟失重对眼结构和视功能影响的研究进展

失重作为一种最主要的太空环境因素,对航天员眼结构和视功能会产生不同程度的影响,不仅涉及航天员自身的眼健康,而且关系到对航天仪器操作的准确性和及时性.综述了模拟失重对动物眼结构和视功能的影响,头低位卧床试验及在轨飞行对人体眼结构和视功能等方面的影响,阐述了失重对眼结构的影响,包括视网膜神经节细胞、血管内皮细胞的凋亡,脉络...     

General equations for optimal selection of diagnostic image acquisition parameters in clinical X-ray imaging

The purpose of this work was to examine the effects of relationship functions between diagnostic image quality and radiation dose on the governing equations for image acquisition parameter variations in X-ray imaging. Various equations were derived for the optimal selection of peak kilovoltage (kVp) and exposure parameter (milliAmpere second, mAs) in computed tomography (CT), computed radiography (CR), and direct digital radiography. Logistic, logarithmic, and linear functions were employed to establish the relationship between radiation dose and diagnostic image quality. The radiation dose to the patient, as a function of image acquisition parameters (kVp, mAs) and patient size (d), was used in radiation dose and image quality optimization. Both logistic and logarithmic functions resulted in the same governing equation for optimal selection of image acquisition parameters using a dose efficiency index. For image quality as a linear function of radiation dose, the same governing equation was derived from the linear relationship. The general equations should be used in guiding clinical X-ray imaging through optimal selection of image acquisition parameters. The radiation dose to the patient could be reduced from current levels in medical X-ray imaging.     

Development of valid pulmonary function equations for trained athletes

The validity of commonly recommended pulmonary function prediction equations (Bulletin Européen de Physiopathologie Respiratoire, Clinical Respiratory Physiology) was tested with two samples (n1 = 156; n2 = 218) of well-trained athletes. Pulmonary function measures (FVC, TLC, RV, FEF25%-75%, FEV1.0, PEF, RV/TCL ratio, FEV1.0/FVC ratio) were typically very reliable but inaccurately predicted with recommended equations based upon anthropometric characteristics. Newly developed "unisex" regression equations were developed with "dummy" coding of gender (i.e., 0 = female; 1 = male), age, height, weight, and various interactions. The new equations were validated with a subsample of group one, cross-validated with the remaining portion of group one, and then cross-validated again with the 218 subjects from sample two. The newly created pulmonary function prediction equations are more valid for well-trained athletes than the equations in use for the general population.     

The estimation of body density in rugby union football players.

The general regression equation of Durnin and Womersley for estimating body density from skinfold thicknesses in young men, was examined by comparing the estimated density from this equation, with the measured density of a group of 45 rugby union players of similar age. Body density was measured by hydrostatic weighing with simultaneous measurement of residual volume. Additional measurements included stature, body mass and skinfold thicknesses at the biceps, triceps, subscapular and suprailiac sites. The estimated density was significantly different from the measured density (P < 0.001), equivalent to a mean overestimation of relative fat of approximately 4%. A new set of prediction equations for estimating density was formulated from linear regression using the logarithm of single and sums of skinfold thicknesses. Equations were derived from a validation sample (n = 22) and tested on a crossvalidation sample (n = 23). The standard error of the estimate (s.e.e.) of the equations ranged from 0.0058 to 0.0062 g ml-1. The derived equations were successfully crossvalidated. Differences between measured and estimated densities were not significant (P > 0.05), total errors ranging from 0.0067 to 0.0092 g ml-1. An exploratory assessment was also made of the effect of fatness and aerobic fitness on the prediction equations. The equations should be applied to players of similar age and playing ability, and for the purpose of identifying group characteristics. Application of the equations to individuals may give rise to errors of between -3.9% to +2.5% total body fat in two-thirds of cases.     

Prediction accuracy of body density, lean body weight, and total body volume equations

The purpose of this study was to determine the accuracy of percent fat estimates derived from regression equations with functions of predicting body density (BD), lean body weight (LBW), and total body volume (TBV) from anthropometric variables. BD, LBW, and TBV equations were derived from the data of 95 young, adult men (percent fat X = 13.4%). The multiple correlations for these equations were: BD, 0.86-0.83; LBW, 0.96-0.95; and TBV, 0.99. The zero order correlations between laboratory determined percent fat and percent fat derived by the BD, LBW, and TBV equations ranged from 0.80 to 0.86 with standard errors from 3.1% to 3.7%. This shows that BD, LBW, and TBV equations have similar accuracy when transformed to percent fat. The derived equations were cross validated with three additional, but diverse, samples (percent fat X = 5.1%; 16.7%; 27.1%). The cross validations results revealed that all equations exhibited similar accuracy. With samples differing in percent fat, systematic prediction errors occurred. The results further confirm population specificity of prediction equations.     

The flaws in tooth root resorption assessment algorithms: the role of source position

OBJECTIVES: The purpose of this project was to analyse the effects of X-ray source location on mathematical compensations used in the clinical assessment of external apical root resorption (EARR). METHODS: Using geometric constructions, governing equations were derived to express the relationships between actual tooth, root and crown lengths, and their image sizes on "before" and "after" radiographs. RESULTS: Good agreement was found between calculated and published experimental results. More importantly, errors associated with the assessment methods are demonstrated. CONCLUSION: It is established that root resorption assessment algorithms cannot reliably compensate for the inherent distortions in radiographic evaluations of EARR, even in the best-case scenario of an idealized, precisely characterized, linear tooth.     

Research design and analysis of data procedures for predicting body density

Statistical methods used to develop body composition prediction equations were examined. Equations published in the 1960s and early 1970s have been called "population-specific" equations because they were developed on homogeneous samples. A major limitation of population-specific equations was a low ratio of subjects per variable, which reduces validity. The more recent method has been to develop "generalized" equations with large samples varying greatly in age and body fatness. The statistical models used for generalized equations were nonlinear regression analysis to account for the quadratic relation between body density and skinfold fat. Age was used as an independent variable to adjust for aging. Generalized equations exhibit accuracy consistent with population-specific equations and increase the generalizability of prediction. Future body composition research should focus on the cross-validation of published equations to define the limits of equation accuracy.     

Reconstruction of femur length from its fragments in South Indian males

Stature is one of the essential parameters in the establishment of identity of an individual. It is well documented from the previous studies that intact femur has the highest correlation with stature and as such widely used in the regression equation derivations. However, the femur is not always recovered intact in forensic cases, thereby rendering the equations derived from the whole bone inappropriate for analysis. This has necessitated the derivation of regression equations for estimating the length of femur, from the fragments of femur. The calculated maximum femoral length can then be used to estimate the stature of the individual by the regression equations, tables or the multiplication factors already established by the various studies. Seven variables were measured in a sample of 60 male femora. All the measurements showed positive degree of correlation. Regression equations for the estimation of maximum length of femur were derived. It is therefore stated that in the absence of intact femur, regression equations derived from the present study can provide a reliable estimate of maximum length of femur in South Indian males and thereby the adult stature.     

采用第一秒用力呼气量占肺活量的百分比对最大呼气流速-容量数值的推导

分别对177例受检者的V_(50)与FEV_(1.0)/FVC(％),V_(25)与FEV_(1.0)/FVC(％)作了相关性分析,求出相关系数(r=0.8428,0.7917;p<0.0005)和直线回归方程式,两者均呈高度正相关。用V_(50)与FEV_(1.0)/FVC(％),V_(25)与FEV_(1.0)/FVC(％)的直线回归方程式对另外48例受检者V_(50)、V_(25)值进行推算。推算出的V_(50)与实测的V_(50)、V_(25)与实测的V_(25)均呈高度正相关(r=0.9321,0.8445;P<0.0005)。同时,对119例受检者其它肺功能指标与推算的V_(50)、V_(25)也作了比较。在其它肺功能正常组中,推算出的V_(50)、V_(25)与其它肺功能符合率分别为94.1％、80.4％,在其它肺功能异常组中,符合率为100％。因此,用此法推算的V_(50)、V_(25)对小气道功能的评价具有较大的可靠性和一定的实用价值。     

Comparison of radionuclide estimation of glomerular filtration rate using technetium 99m diethylenetriaminepentaacetic acid and chromium 51 ethylenediaminetetraacetic acid

Simultaneous measurements of the clearance rates of technetium 99m diethylenetriaminepentaacetic acid (99mTc-DTPA) and chronium 51 ethylenediaminetetraacetic acid (51Cr-EDTA) were performed in 30 patients with a range of renal function (glomerular filtration rates between 9 and 120 ml/min). Using multiple blood samples, the two clearance values correlated well (r = 0.991, standard error 3.9 ml/min), but DTPA clearance was systematically higher by 7.6%. For each radiopharmaceutical, an equation was derived to correct clearance values obtained using only plasma samples taken at 2 and 4 h for the systematic error inherent in this technique compared with analysis of the complete plasma concentration-time curve. The root mean square error remaining after application of these equations was 1.9 ml/min for both the EDTA and DTPA data. The corresponding errors obtained using the equation derived by Brochner-Mortensen for EDTA plasma clearance were 2.2 ml/min and 1.9 ml/min, respectively, these values were not significantly different from those obtained using the equations derived in this study.     

The application of the linear-quadratic dose-effect equation to fractionated and protracted radiotherapy

The linear-quadratic (LQ) dose-effect formalism is currently providing new perspectives into the ways in which alterations in the dose per fraction in conventional radiotherapy may be used to bring about improved results with respect to early or late normal tissue reactions. In this paper, using a model initially developed by Roesch, the LQ equations are explored further in terms of dose-rate rather than dose. By the incorporation of one other parameter, mu, which relates to the rate of repair of sub-lethal radiation damage, a more general formalism is obtained. In particular, equations are derived which can be used to examine the relative effectiveness of different treatment regimes, including those involving decaying sources. Such equations are of wider applicability than other LQ derivations which relate only to dose-response relationships. The extended equations, which are fully consistent with the existing LQ method, are also shown to lead directly to other independently established, relationships for protracted irradiation. The nature of the link between high and low dose-rate treatments is discussed, and some worked examples provide indications of how the new equations may be used to assess further the potential clinical benefits of low dose-rate treatments and permanent implants.